1. Field of the Invention
The present invention relates to a composition, a light reflecting film, a luminance-improving film, a backlight unit, and a liquid crystal display device. In more detail, the present invention relates to a composition, a light reflecting film using the composition, a luminance-improving film using the light reflecting film, a luminance-improving film-attached backlight unit using the luminance-improving film, and a liquid crystal display device using the luminance-improving film.
2. Description of the Related Art
The applications of a flat panel display such as a liquid crystal display device (hereinafter, also referred to as LCD) as an image display device which has low power consumption and is space-saving are expanding year by year. A liquid crystal display device has a configuration in which a backlight (hereinafter, also referred to as BL), a backlight side polarizing plate, a liquid crystal cell, and a viewing side polarizing plate are provided in this order.
In recent years, in flat panel display markets, development in power saving has been progressing as LCD performance improvement. This performance improvement has been significantly seen in liquid crystal display devices having a small size, such as, in particular, tablet PCs, smartphones, or the like.
On the other hand, in a large-size device for TV applications, development of a next generation high-definition television (4K2K, EBU ratio of 100% or greater) for the current TV standard (FHD, NTSC (National Television System Committee) ratio of 72%≈BU (European Broadcasting Union) ratio of 100%) has been progressing, and development in power saving has been progressing as performance improvement equivalently to that in a small-size device. Thus, there has been increasing demand for power saving in a liquid crystal display device.
With power saving for a backlight, it has been proposed to provide a reflective polarizer between a backlight and a backlight side polarizing plate. A reflective polarizer is an optical element which transmits only light oscillating in a specific polarization direction and reflects light oscillating in other specific polarization directions, form light incident while oscillating in all polarization directions. Thus, it is possible to recycle the light reflected without being transmitted through the reflective polarizer, and it is possible to improve the light use efficiency in the LCD.
As the reflective polarizer, a light reflecting layer formed by fixing a cholesteric liquid crystalline phase which is a reflective polarizer reflecting only circular polarization in one direction is known.
As an example of the light reflecting layer formed by fixing a cholesteric liquid crystalline phase, in JP2013-195630A, a light reflecting film which has two or more layers of a film formed by fixing a liquid crystal phase after a curable liquid crystal composition is applied on the film formed by fixing the liquid crystal phase after a resin film or a curable liquid crystal composition is applied, is transparent, and includes a surfactant having a specific structure in which a curable liquid crystal composition has a hydrogen bonding group and a fluoroalkyl chain is described. In the examples of JP2013-195630A, only examples of a light reflecting film obtained by using a rod-shaped liquid crystal compound are disclosed, but in JP2013-195630A, a light reflecting layer using a discotic liquid crystal compound is also described.
In JP1998-307208A (JP-H10-307208A), a manufacturing method of an optical film in which a discotic liquid crystalline material having a chiral discotic nematic phase is rapidly cooled at a cooling speed of 100° C./min or greater from a temperature region in which this liquid crystal phase is exhibited, and then subjected to a photocrosslinking reaction is described. In the examples of JP1998-307208A (JP-H10-307208A), an optical film obtained by using a liquid crystal composition including a discotic liquid crystal compound with chirality and another discotic liquid crystal compound is disclosed. In particular, in Example 4, a red light reflecting film having a film thickness of 10 μm and a reflecting center wavelength of 640 nm is disclosed.
In JP2000-171637A, an optical compensation sheet having an optically anisotropic layer including a polymer formed of a non-chiral discotic liquid crystal compound having a polymerizable group and a chiral compound is described. In the examples of JP2000-171637A, an optically anisotropic layer obtained by using a liquid crystal composition including a discotic liquid crystal compound without chirality and a discotic liquid crystal compound with chirality is disclosed.